Patent GB-972162-A (GB)
Title: Method for automatically determining the magnitude of particles and counting same
IPC: G01N15/10
Filed: 1962-03-29
Abstract: 972,162. Counting particles; gauging apparatus. BROWN, BOVERI & CO. Ltd. March 29, 1962 [March 30, 1961; Feb. 6,1962], No. 12071/62. Headings G1N and G1M. In a method of counting a number of particles and determining their magnitudes, a photographic image of a particle collection is prepared in which the images of the particles are in the form of electrically conductive surfaces on an insulating medium, the reverse side of which carries a conductive layer and the conductive images, which with this basic conduction layer form a plurality of capacitors, are sequentially charged during a scanning process, the charging pulse amplitudes and their number being recorded. In the arrangement of Fig. 1 the photographic image is mounted with its base layer 1 in contact with a conduction turntable 4, and a pointed charging electrode 5 energized by source 6 is caused to scan the rotating image by being moved by a lead screw in a direction at right angles to the axis of rotation. Contact is made by a brush 7, and the charging current pulse magnitude is made proportional to the particle size by a capacitor C, having a capacity large compared with that of the particles, which is connected in series with the source 6. A resistor R in parallel with capacitor C controls the dying out time of impulses and damps any spurious oscillation which may be induced by the impulses. The impulses are applied to a counter 10 via an amplifier 8 and an amplitude discriminator 9. The charging electrode 5 employs a high charging potential (2200V) and is not in contact with the surface being scanned, but an alternative arrangement using a wire in direct contact with the surface is described, the wire being of aluminium having an oxide film which is just punctured or penetrated by the D.C. voltage. The wire may be periodically replaced, or a scanning arrangement, described with reference to Figs. 2 and 3 (not shown), in which a loop of oxidised wire between a spool and a take up drum is renewed by being fed forward at the end of each double journey can be provided. In this arrangement the particle images are discharged on the return journey by a precious metal slide wire which is lowered when the carriage reaches its outer limit. The image capacitor may be produced by copying on a high resolving power film, and transferring this copy to a water soluble optically sensitive layer on a polystyrene or polymethyl methacrylate film the parts not covered by particle images being hardened so that they are not removed during a subsequent washing. Conductive material painted on adheres to the unhardened parts only, to produce conductive particle images. Alternatively a stencil may be prepared through which an insulating base can be sprayed with a metal emulsion e.g. a silver solution or through which a vapourised metal can be applied under vacuum. The base conductor may be similarly applied. The particle images may be scanned by moving the film in one direction and by traversing the scanning head at right angles. The system described has the advantage that each particle gives rise to only one charging impulse.